The present invention relates to utility knives, and more particularly to utility knives having retractable blades and in which the blades may be changed quickly in use.
Utility knives having replaceable blades and with a variety of end uses are well known in the art. Exemplary of such utility knives are U.S. Pat. Nos. 3,107,426, 3,872,591, 3,577,637, 4,242,795, 4,586,256, and 4,663,845. Such knives incorporate a blade carrier which mounts and supports a blade in the interior of the knife handle. The blade carrier may also incorporate a thumb actuated button that is depressed to unlatch the blade carrier and blade from one of several latched positions and then moved forwardly or rearwardly to extend or retract the blade.
As use of the blades causes them to dull, the blades need to be replaced on a fairly frequent basis. The respective knives are adapted so that mounting and replacement of the blades is relatively simple. For example, in many instances, the knife comprises a pair of complementary halves which are held together by a screw or the like. Loosening or removal of the screw permits the knife to be disassembled and the blade accessed. However, even this relatively simple operation becomes tedious and time consuming for the user.
However, while such knife designs generally operate in an efficient manner, one continuing problem with them has been the tendency of the blades to release or disengage from the blade carrier during heavy use, particularly where strong lateral or twisting forces are imposed on the cutting edge of the blade. The twisting or lateral movement of the blade may cause the nose of the matching knife halves to open slightly, as the knife handle halves are typically secured only at their midpoint by a single screw. This, in turn, may permit the blade to release from the blade carrier and the knife handle, resulting in the need to stop using the knife and to reassemble the knife and blade. The release of the blade from the knife during use also potentially poses a safety problem.
Other utility knives have utilized designs where one portion of the knife handle is wedged into position and locked with a bolt with a knurled head for finger operation located at the rear of the knife. Still other utility knives have utilized designs where the matching knife handle halves are rotatable about their midpoints to open the knife and expose the blade for removal. Such knives typically also include some type of locking mechanism in the knife handle to insure that the handle halves do not rotate and open the knife accidentally. However, these knife designs suffer from their complexity both in the number of parts required for the knife as well as in their manufacturing and assembly.
Accordingly, a need still exists in the art for a utility knife design which is both simple to manufacture, has a minimum number of parts, and yet provides the user with the ability to remove and change blades quickly.